1. Field of the Invention
The invention relates generally to switching power supplies and, more particularly, the invention relates to a switching power supply having a low power burst mode.
2. Description of Related Technology
Generally speaking, a switching power supply (SPS) provides a cost-effective and energy-efficient device for converting energy from a single direct current (TC) supply voltage into one or more DC output voltages that have a greater or lesser magnitude than the supply voltage. SPSs are commonly used to power electronic devices, particularly battery powered devices such as portable cellular telephones, laptop computers, etc., that have a normal operating mode, in which the devices consume a relatively large amount of power, and a standby operating mode (e.g., a sleep mode), in which the devices consume relatively little power. Typically, these electronic devices automatically reenter the standby operating mode when a user has not interacted with the device for a predetermined amount of time and automatically enter the normal operating mode when the user interacts in some manner with a control button, mouse, etc. of the device.
In conventional electronic devices, a standby operating mode is accomplished by either reducing the output voltage of the power supply within the devices or, alternatively, establishing a source of auxiliary power for the devices. However, both of these conventional approaches are undesirable because they require additional components, which results in higher production costs, and because there is an output voltage below which the device will not function, thereby limiting the amount that the power consumption of the device can be decreased. Additionally, when using a conventional SPS in a standby operating mode, a substantial switching loss occurs within the SPS despite any reduction in power consumption due to a reduced output voltage. More specifically, a conventional SPS varies the duty cycle of a power switch (e.g., a transistor) to compensate for changes in power requirements at the output of the supply and operates at a predetermined frequency regardless of the amount of power supplied. As a result, the power switch within a conventional SPS operating in a standby mode changes states (i-e., turns on and off) at the same rate as when the SPS is operating in a normal mode. In the standby operating mode, these switching transitions consume a significant amount of power, which significantly increases the lower limit of power consumption in the standby mode.